Anti-freeze peptides (AFPs) have been suggested for improving the freezing tolerance of foodstuffs. In particular it has been suggested that some AFPs may be capable of increasing the smooth texture of frozen food products such as ice cream. Up till now, however the use of AFPs has not been applied to commercially available food products. One reason for this is that up till now it has proved difficult to reproducibly produce a frozen food product having the desired texture and eating characteristics.
WO 90/13571 discloses antifreeze peptides produced chemically or by recombinant DNA techniques from plants. The AFPs can suitably be used in food products such as ice cream. No guidelines are given as to how to obtain smooth textures.
WO 92/22581 discloses AFPs from plants, which can be used for controlling ice crystal growth. This document also describes a process for extracting a polypeptide composition from intercellular spaces of plants by infiltrating leaves with an extraction medium without rupturing the plant cells.
Applicants believe that one of the possible reasons for the lack of desired texture in frozen food products containing AFP is that although the AFP is capable of recrystallisation inhibition it is often not capable of avoiding less favourable hard and brittle textures. Applicants believe that one of the explanations for this is that AFPs seem capable of controlling the growth of the ice-crystals. However the presence of AFP may also lead to an adverse effect in that the ice crystals tend to form aggregates leading to hard and brittle products. Thus the texture of the product is unfavourably affected during the manufacturing process.
The present invention therefore aims at defining manufacturing conditions which improve the texture of AFP containing frozen food products.
Surprisingly it has now been found that if the conditions for producing the frozen food material are carefully chosen, this leads to an improved texture. In particular applicants have found that if the production process includes the use of one or more of the following steps;
(i) a (pre-)freezing step which is a nucleation dominated freezing process;
(ii) a (post-)compaction step using a screw extruder or a (piston) compactor;
this leads to aggregation of the ice crystals being minimised and therefore results in more favourable textures of the frozen product, said texture being maintained for prolonged storage periods.
Generally in the freezing of a composition, two distinct phases can be seen: at the onset of the freezing process many small ice crystals are rapidly formed. This phase is called the nucleation phase of the freezing process. Following the nucleation process the remaining part of the composition freezes onto the surface of the nucleates and therewith contributes to the growth of the ice crystals. This phase in the freezing process is called the growth phase. In a growth dominated freezing process most of the composition is frozen during the growth phase, in a nucleation dominated freezing process most of the composition is frozen during the nucleation phase.
Traditional freezing processes for frozen confectionery products for example involves the use of scraped surface heat exchangers whereby the mix to be frozen is subjected to shear during the freezing process. Generally this freezing process takes from 5 to 30 minutes for the product to reach a temperature of −5° C. or lower. In this process initially some nucleation of ice crystals occurs followed by a period wherein ice crystal growth dominates.
Alternative freezing processes, which for example are used for the freezing of water ice involves the low shear or quiescent freezing of the mix, for example by filling a mould and dipping the mould into a cold bath, for example filled with brine. In this process initial nucleation of ice crystals takes place at the surface of the mould, the internal of the product then tend to freeze more slowly in a freezing process dominated by growth.
Applicants have now surprisingly found that the aggregation in AFP containing products can significantly be reduced if a nucleation dominated freezing process is chosen. Such a freezing process is generally characterised by a short freezing time in combination with the formation of small ice crystals. Preferably the freezing process is carried out under low shear or quiescent freezing conditions.